Intake valve for a high-pressure pump, in particular for internal combustion engine fuel

ABSTRACT

The valve ( 9 ) has a valve body ( 36 ) having a seat ( 42 ) with which cooperates a shutter ( 43 ) kept closed by a first spring ( 48 ) of substantially constant pressure, and by a second spring ( 49 ) varyuing in pressure during at least part of the stroke of the piston ( 7 ). The springs ( 48, 49 ) are helical compression types, and their pressures are summed on the shutter ( 43 ), which has a plate ( 44 ) and a stem ( 46 ). The first spring ( 48 ) is located between the valve body ( 36 ) and a flange ( 52 ) integral with a sleeve ( 53 ) which is fitted to the stem ( 46 ) in an adjustable position; and the second spring ( 49 ) is located between the plate ( 44 ) and the piston ( 7 ).

TECHNICAL FIELD

The present invention relates to an intake valve for a high-pressurepump, in particular for internal combustion engine fuel.

BACKGROUND ART

As is known, the fuel injected into internal combustion engine cylindersmust be compressed to around 1600-bar pressure. Modern feed systemscomprise a high-pressure piston pump for feeding the compressed fuel toa common rail communicating with the various engine injectors, and whichin turn is supplied with fuel at around 5-bar pressure by a low-pressurepump.

Each pump cylinder has an intake valve comprising a shutter normallyclosed by a spring, and which opens the valve when the difference in thefuel supply pressure in the cylinder exceeds the force or pressureexerted by the spring on the shutter.

The pump normally comprises a group of radial pistons, e.g. threepistons spaced 120° apart, which are activated by a common cam actuatorfitted to a shaft; and each shutter spring is appropriately calibrated,but so located that its pressure is unaffected by the position of therelative piston.

The above known intake valve (valve 1) has various drawbacks, byresulting in unbalance of both the operating shaft and the deliverypressure of the cylinders when low flow, e.g. less than 30% of maximumflow, is demanded of the pump.

That is, the delay with which the various valves open varies, so thatthe pistons compress different amounts of fuel. In very low flowconditions, as when the engine is run at idling speed, some of thevalves may not even open at all, so that unbalance of the operatingshaft of the pump is considerable and greatly reduces the working lifeof the pump. Moreover, given its high elastic constant, the spring canonly be calibrated within a tolerance range relatively wide.

To reduce the unbalance on the pump caused by the intake valve describedabove, a high-pressure pump has recently been proposed in which theshutter spring is located between the shutter and the piston (valve 2),so that, during the intake stroke of the piston, the pressure of thespring is reduced rapidly, while still allowing the valve to open.

The above known valve 2 has a valve body with a substantiallytruncated-cone-shaped lateral surface. The valve body is fixed to thecylinder by a ring nut acting on the lateral surface, and has an intakeconduit sloping with respect to the valve body axis.

This known valve 2 also has several drawbacks. In particular, theshutter spring has a high elastic constant and therefore requires aconsiderable pressure drop to open; on account of its location, thespring cannot be calibrated, so that numerous versions of the springmust be provided for different applications; the shape of the valve bodymakes automated preassembly of the valve difficult; and, finally,location of the intake conduit weakens the valve body, which, in use, issubject to cracking.

From document U.S. Pat. No. 5,701,873, it is also known a piston pumphaving a coaxial intake valve, the shutter of which is kept closed bythe sum of pressures of two different helical compression springs. Oneof these springs is relatively strong and permanently exerts a closingpressure on the shutter, whereas the other spring is relatively weak andis supported on a spring plate, which is axially displaceable in achamber communicating with the intake fluid for damping purpose.

DISCLOSURE OF THE INVENTION

It is an object of the invention to provide a high-pressure pump intakevalve enabling calibration of the opening pressure of the shutter, andwhich is easy to preassemble, is highly reliable and durable, andeliminates the aforementioned drawbacks typically associated with knownintake-valves.

According to the present invention, there is provided an intake valvefor a high-pressure pump, in particular for internal combustion enginefuel, having at least one cylinder, and a corresponding piston slidingtherein through an intake stroke and a compression stroke; said valvecomprising a seat coaxial with said cylinder and cooperating with anaxially movable shutter; and a pair of compression helical springs forkeeping closed said shutter, said shutter being opened during saidintake stroke in opposition to the sum of pressures of said springs; afirst one of said springs being a substantially constant pressure, saidconstant pressure being adjustable; a second one of said springs beinglocated between said shutter and said piston so that the relevantpressure decreases sinusoidally during said intake stroke and increasessinusoidally during said compression stroke.

More specifically, the pressures of the two springs are summed on theshutter, and the pressure of the first spring is adjustable; said seatis carried on the valve body; the shutter is a mushroom type having aplate engaging said seat, and a stem extending in an opposite directionto the piston; the two springs are helical compression types; the firstspring is located between the valve body and a flange fixed to the stemin an axially adjustable position; the second spring is located betweenthe plate and the cylinder; and the ratio between the pressure of thefirst spring and that of the second spring at the bottom dead centerposition of the piston ranges between 1.5 and 6.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred, non-limiting embodiment of the invention will be describedby way of example with reference to the accompanying drawings, in which:

FIG. 1 shows a diagram of a radial-piston pump, for internal combustionengine fuel, in which each cylinder is equipped with an intake valve inaccordance with the invention;

FIG. 2 shows a partial longitudinal section of a cylinder of the FIG. 1pump;

FIG. 3 shows a larger-scale detail of FIG. 2;

FIG. 4 shows a graph of the opening pressure of the pump intake valves;

FIG. 5 shows a graph of the opening pressure of the intake valveaccording to the invention as compared with that of a known valve;

FIG. 6 shows a partial longitudinal section of a known intake valve.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIG. 6, a known high-pressure pump comprises acylinder a in which slides a piston b; and an intake valve c (valve 2)carried by a valve body d having a truncated-cone-shaped lateralsurface. Valve c is defined by a mushroom-shaped shutter comprising aplate e coaxial with cylinder a and guided inside a hole f in valve bodyd. A spring g is located between plate e and a shoulder of piston b, andacts variously on plate e during the stroke of piston b.

Spring g must provide a given opening pressure also at the bottom deadcenter position of piston b, and therefore has a high elastic constant.Valve body d is fixed to cylinder a by a threaded ring nut h having acavity complementary in shape to that of body d, and has an intakeconduit i which must leave the edge of ring nut h free. Intake conduit itherefore slopes, and forms in valve body d a weak region m which iseasily cracked as a result of the impact of plate e.

With reference to FIG. 1, number 5 indicates as a whole a high-pressurepump for internal combustion, e.g. diesel, engine fuel. Pump 5 is aradial-piston type, and comprises three cylinders 6 spaced 120° apart,and in each of which slides a corresponding piston 7. The threecylinders 6 are carried by a common pump body, which forms a closedcentral operating chamber housing a cam actuator 8 carried by a shaft 10and common to all three pistons 7.

Each cylinder 6 is equipped with an intake valve indicated as a whole by9; and with a delivery valve 11. The three intake valves 9 are suppliedby a low-pressure pump (not shown) by means of a feed conduit 12, anelectromagnetic proportional inlet valve 13, and three inlet conduits14.

The three delivery valves 11 are connected to three correspondingdelivery conduits 16 communicating with a high-pressure fuel common rail17, which supplies a series of injectors 18 of the internal combustionengine cylinders in known manner. Injectors 18 are controlledelectromagnetically but-activated in known manner by the pressurizedfuel in common rail 17.

Common rail 17 is fitted with an overpressure valve 15 by which anysurplus fuel is drained into a return conduit 21 at atmosphericpressure; the fuel used to operate injectors 18 is also fed to returnconduit 21; and, to lubricate the bearings of shaft 10 and the contactsurfaces of cam actuator 8 and pistons 7, feed conduit 12 supplies acertain amount of fuel into the central chamber of the pump body via achoke 22 and an overpressure valve 23.

The lubricating fuel from both the central chamber and overpressurevalve 23 is fed to return conduit 21. To dispose of fuel leakage throughproportional inlet valve 13, the incoming fuel pressure is greater thanthe return pressure, and inlet conduits 14 communicate with returnconduit 21 via a choke 24.

High-pressure pump 5 is normally supplied by the low-pressure pump withfuel at around 5-bar pressure, and supplies common rail 17 with around1600-bar pressure; and the intake valve 9 of each cylinder 6 should becalibrated to open at a roughly 1.8-bar pressure drop, but with aroughly 0.01-bar tolerance.

With reference to FIG. 2, pump 5 comprises a pump body 26 with threecylinders 6 (only one shown). In each cylinder 6 slides a correspondingpiston 7, which is pushed towards cam actuator 8 (see also FIG. 1) by acorresponding compression spring 27, so that, as cam actuator 8 rotates,the three pistons 7 are activated sequentially to perform an intakestroke between a top dead center position and a bottom dead centerposition, and a compression stroke in the opposite direction; bothstrokes being performed in harmonic motion. More specifically, theintake stroke is performed negatively by spring 27, and the compressionstroke positively by cam actuator 8.

Delivery conduit 16 of each cylinder 6 (see also FIG. 3) comes outinside cylinder 6 through a hole 28 forming a conical seat 29 fordelivery valve 11, which comprises a ball shutter 30 pushed against seat29 by a compression spring 31. At the outer end, each cylinder 6communicates with a coaxial cylindrical opening 32, which is larger indiameter than cylinder 6, has a threaded axial portion 33, and forms anannular shoulder 34 with cylinder 6.

Intake valve 9 of each cylinder 6 comprises a valve body 36 defined by acylindrical plate. Valve body 36 is housed inside opening 32 and heldresting on shoulder 34 by a threaded ring nut 37 having a projectingedge 35 at the bottom, and a hexagonal socket 38 at the top for an Allenwrench.

Using an Allen wrench, and with the interposition of a low-pressure fuelseal 39, ring nut 37 is screwed inside threaded portion 33 of opening 32until edge 35 effectively forces valve body 36 against shoulder 34, sothat valve body 36 forms the end surface of cylinder 6.

Intake valve 9 comprises an opening 41 formed in valve body 36 andforming at the bottom a conical seat 42 coaxial with cylinder 6. Conicalseat 42 is closed by a mushroom-type shutter 43, which comprises a plate44 carried by a cylindrical stem 46 extending in the opposite directionto piston 7 and housed in a cavity 40 in ring nut 37. Plate 44 has aconical annular surface 45 hermetically engaging conical seat 42; andshutter 43 is movable axially between a closed position closing seat 42(FIG. 2), and an open position opening seat 42. For which purposeopening 41 comprises an axial portion 47 for axially guiding stem 46 ofshutter 43.

According to the invention, shutter 43 is kept in the closed position byelastic means comprising a first spring 48 and a second spring 49: thefirst spring 48 acting on shutter 43 with substantially constant forceor pressure during the movement of the corresponding piston 7; and thesecond spring 49 acting on shutter 43 with a pressure varying during atleast a portion of the movement of piston 7. More specifically, bothsprings 48 and 49 are helical compression types and act on shutter 43 bysumming the respective pressures.

First spring 48 is located between a recess 51 of opening 41, in the topsurface of valve body 36, and a flange 52 carried by a sleeve 53 fixedto stem 46 of shutter 43. More specifically, sleeve 53 has an insidediameter interfering slightly with the outside diameter of stem 46, andis force-fitted onto stem 46 in an adjustable position, so as tocalibrate the pressure of spring 48 extremely accurately.

Second spring 49 is located between plate 44 and piston 7. For whichpurpose, plate 44 has an underside recess 54 on which one end of spring49 rests, and piston 7 has a smaller-diameter portion 56 forming ashoulder 57 on which rests the other end of spring 49. In the top deadcenter position of piston 7, the free end of portion 56 is obviouslypositioned a given minimum distance from the bottom surface of plate 44,so that the pressure of spring 49 on plate 44 therefore decreasessinusoidally during the intake stroke of piston 7, and increasessinusoidally during the compression stroke of piston 7.

Hole 28 of delivery conduit 16 comes out inside cylinder 6 at portion 56of piston 7, when the piston is in the top dead center position as shownin FIG. 3. Inlet conduit 14 of intake valve 9 comprises a radial hole 58of cylinder 6, which comes out inside the corresponding cylindricalopening 32 of cylinder 6 at valve body 36. For which purpose, thelateral surface of valve body 36 has a recess 59 which, together withthe lateral wall and shoulder 34 of opening 32, forms an annular channel60. Inlet conduit 14 also comprises a radial hole 61 of valve body 36,which comes out inside an annular groove 62 of opening 41.

The pressure exerted by first spring 48 is less than that of secondspring 49, and is preferably selected as low as possible to reduce itselastic constant.

For intake valve 9 to open when the fuel pressure in cylinder 6 fallsbelow a value ranging between 1.3 and 5 bars, the total pressure onplate 44 is obtained by adding the pressures of first spring 48 andsecond spring 49 with a ratio ranging between 1.5 and 6. Morespecifically, with a roughly 2.3-bar total pressure value, first spring48 may be designed to ensure a roughly 1.8-bar constant pressure onplate 44, and second spring 49 may be designed to vary in pressure so asto ensure a 0.5-bar intake opening pressure on plate 44. Tests haveshown that, with the above pressure values of springs 48 and 49, spring48 can be calibrated between 1 and 5 bars, with a tolerance of ±0.05bar.

Accordingly, the ratio of the elastic constant of first spring 48 tothat of second spring 49 may range between 1 and 20. Advantageously, theelastic constant of the first spring may be less than 1 N/mm, e.g.between 0.1 N/mm and 0.8 N/mm, and that of second spring 49 may bearound 0.07 N/mm.

Operation of pump 5 and intake valve 9 is obvious, and thereforerequires no further explanation. In FIG. 4, each curve A, B and C shows,as a function of the rotation angle of shaft 10, the opening pressurerequired by plate 44 for variable spring 49 of corresponding intakevalve 9 for pump 5; line D shows the nominal constant opening pressurerequired for constant spring 48; and the maximum and minimum pressuredifferences of the three variable springs 49 depend on various factors,and must fall within the range indicated by lines E and F.

In FIG. 5, curve G shows the opening pressure required by plate 44 as afunction of the rotation angle of shaft 10, when plate 44 is kept closedby two springs 48 and 49; and line H shows the constant opening pressureof known valve 1.

Curve M, on the other hand, shows the variable pressure of spring g inFIG. 6, i.e. the pressure required by the plate of known valve 2. As canbe seen, much less force is required of spring 49 than spring g in FIG.6, so that spring 49 can be made of smaller-diameter music wire, thusgreatly reducing its size and elastic constant. The lower elasticconstant of spring 49 reduces the mean opening pressure of valve 9, thusincreasing fuel intake into the cylinder and improving the efficiency ofpump 5.

The advantages of the intake valve according to the invention, ascompared with those of known pumps, will be clear from the foregoingdescription. In particular, neither spring 48 nor spring 49 generatesthe entire opening pressure of valve 9, so that both have a lowerelastic constant; constant spring 48 can be calibrated easily to meetthe requirements of different applications; variable spring 49 may havea low elastic constant, thus reducing its size about portion 56 ofpiston 7; the cylindrical shape of valve body 36 and the radial locationof hole 58 do not overly weaken valve body 36, thus reducing the risk ofin-service cracking; and, finally, to fit valve 9 to respective cylinder6, the valve 9 assembly, defined by valve body 36, shutter 43, spring 48and sleeve 53, can be preassembled easily.

Clearly, changes may be made to the intake valve as described hereinwithout, however, departing from the scope of the accompanying claims.For example, valve body 36 may have more than one radial hole 58; theratios between the elastic constants of springs 48 and 49, or therespective absolute values, may be different; and variable-pressurespring 49 may be designed to only vary in pressure during part of therelative piston stroke.

Given the possibility of calibrating spring 48, the same springs 48, 49can be used for mass producing intake valves 9 for different pump 5models, thus reducing manufacturing cost; pump 5 may have a differentnumber of cylinders 6, which may be activated by independent actuators;and finally, each piston 7 may be activated positively at both strokes,e.g. by a connecting rod and crank mechanism.

1. An intake valve for a high-pressure pump, in particular for internalcombustion engine fuel, having at least one cylinder (6), and acorresponding piston (7) sliding therein through an intake stroke and acompression stroke; said valve (9) comprising a seat (42) coaxial withsaid cylinder (6) and cooperating with an axially movable shutter (43);and a pair of compression helical springs (48, 49) for keeping closedsaid shutter (43), said shutter (43) being opened during said intakestroke in opposition to the sum of pressures of said springs (48, 49); afirst one of said springs (48, 49) being of a substantially constantpressure, said constant pressure being adjustable; a second one of saidsprings (48, 49) being located between said shutter (43) and said piston(7) so that the relevant pressure decreases sinusoidally during saidintake stroke and increases sinusoidally during said compression stroke.2. A valve as claimed in claim 1, wherein said seat (42) is carried by avalve body (36) closing said cylinder (6); and said shutter (43) is amushroom type having a plate (44), and a steam (46) extending in anopposite direction to said piston (7); characterized in that said firstspring (48) is located between said valve body (36) and a flange (52)fixed to said stem (46) in an adjustable axial position so as tocalibrate accurately the pressure of said first spring (48), said secondspring being located between said plate (44) and said piston (7).
 3. Avalve as claimed in claim 1, characterized in that, for a total openingpressure of the valve (9) of 1 to 4 bars, the ratio between the constantpressure of said first spring (48) and the pressure of said secondspring (49) at the bottom dead center position of said piston (7) rangesbetween 1.5 and
 6. 4. A valve as claimed in claim 2, characterized inthat said first spring (48) is adjustable within a range of 1 to 5 bars.5. A valve as claimed in claim 3, characterized in that the ratiobetween the elastic constant of said first spring (48) and the elasticconstant of said second spring (49) ranges between 1 and
 20. 6. A valveas claimed in claim 5, characterized in that the opening pressuresprovided by said first spring (48) and said second spring (49) are inthe order of 1.8 and 0.5 bar respectively.
 7. A valve as claimed inclaim 6, characterized in that the elastic constant of said first spring(48) is less than 1 N/mm, and the elastic constant of said second spring(49) is in the order of 0.07 N/mm.
 8. A valve as claimed in claim 3,characterized in that said flange (52) is integral with a sleeve (53)which is fitted to said stem (46) in said adjustable position.
 9. Avalve as claimed in claim 8, characterized in that the position of saidsleeve (58) on said stem (46) is so adjustable that the opening pressuregenerated by the first spring (48) can be calibrated with a tolerance ofat least ±0.05 bar.
 10. A valve as claimed in claim 10 or 11 claim 8,wherein said seat (42) is coaxial with said cylinder (6) and has atruncated-cone-shaped surface engaged by a correspondingtruncated-cone-shaped surface (45) of said plate (44); characterized inthat said plate (44) has a diameter substantially equal to that of saidpiston (7); said second spring (49) being housed between a recess (54)in said plate (44) and a shoulder (57) formed on a smaller-diameterportion (56) of said piston (7).
 11. A valve as claimed in claim 10,wherein said seat (42) is carried by an opening (41) in said valve body(36); said opening (41) comprising a portion (47) for guiding said stem(46); characterized in that said valve body (36) is defined by acylindrical plate (36); said cylinder (6) being provided with an inletconduit (14) comprising a radial hole (61) in said cylindrical plate(36); said radial hole (61) communicating with an annular groove (62) ofsaid portion (47) of the opening (41), and with an annular channel (60)defined by a recess (59) in said cylindrical plate (36).
 12. A valve asclaimed in claim 11, characterized in that said cylindrical plate (36)is fixed inside a cylindrical opening (32) coaxial with said cylinder(6); a threaded ring nut (37) having a projecting annular edge (35) forengaging a flat surface of said cylindrical plate (36).
 13. Ahigh-pressure pump having an intake valve as claimed in claim 10,characterized in that said cylinder (6) has a delivery valve (11)located at said smaller-diameter portion (56) and communicating with apressurized-fuel common rail (17) for supplying a series of fuelinjectors (18).
 14. A pump as claimed in claim 13, characterized in thatthe pump (5) is provided with three radial cylinders (6) each one havinga corresponding inlet conduit (14), and with a common cam actuator (8)for activating the corresponding pistons (7) in sequence; said inletconduits (14) communicating with a return conduit (21), forrecirculating fuel from said pump (5) and/or from said common rail (17),via a choke (22) for controlling the fuel pressure in said inletconduits (14).